In modern vehicle transmissions subject to high loads, the transmission lubricant has to be cooled to temperatures that are uncritical for the system. In particular, in surroundings with high ambient temperatures and for vehicles in which the transmission is encapsulated for noise reduction reasons, cooling devices are accordingly provided in the form of heat exchangers. Heat exchangers are normally used for additional cooling of the transmission lubricant, but may also be used for warming up the transmission lubricant.
The currently known heat exchangers are either oil/air or oil/water heat exchangers and are mounted as additional components at a suitable location in the vehicle. Oil/water heat exchangers may also be integrated in the engine cooling system of the vehicle.
DE 103 15 684 A1 discloses a transmission having a transmission housing, which comprises a region, in which the gear wheels rotate. The transmission also has a heat exchanger which absorbs the heat generated in the transmission and transferred to the transmission lubricant and releases it to a coolant for transporting the heat away from the transmission. In the transmission housing, outside of the region in which the gear wheels rotate, a recess is provided through which lubricant flows and in which the heat exchanger is arranged. One version of the embodiment shows that a bypass valve is provided at the intake side of the pump transporting the transmission lubricant which enables the heat exchanger to be bypassed when the temperatures of the transmission lubricant drop below a specified limit.
The disadvantages of the prior art are, among other things, that additional interfaces are necessary for the constructively separated bypass valve which have to be sealed against leaks. Moreover, a bypass which is constructively separated from the heat exchanger and the power train to be cooled or warmed up requires appropriate constructive efforts and consequently also additional manufacturing costs.
The object of the present invention is to design a cooling system that is more efficient and to eliminate the disadvantages of the prior art.
This object is attained by a generic transmission comprising a heat exchanger with an integrated bypass valve.